You need to take the truck to a good alignment shop and get it checked out. Without a reference on what the caster angle is now, there's no way to tell whether it needs more or less caster. If there has been a radical change in ride height, which is the reason most people install non-stock springs, the alignment could be off in a big way. If the steering does not try to return to center after a turn, you probably need more positive caster angle, but that's not a substitute for proper wheel alignment.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!